Apparently I'm not the only one to get bit by this so I thought I'd mention it here. Acrobat Reader 8.x may on its own or when you request an update, fire off its updater, which may get stuck and eat 100% of the CPU (with or without visible UI). You can't kill it using Task Manager. The only fix I've found is to restart the PC. Feh.

So you go to c:\Program Files\Adobe\Reader 8.0\Reader\plug_ins

You find Updater.api and rename it to something sane like Updater.Die.Horribly.Die.Painfully.Go.Away.And.Die .Brutally.Die.DIE

Or something a bit shorter if you like. Just lose the .api extension.

Now it won't try to update itself, of course, but if you were having this problem to begin with, it wasn't updating itself anyhow, most likely. IAC, you can always rename the file back to .api and let it play.